Safety improvements by an Accident Management strategy of Russian VVER-1000 reactor type

The scope of the present work is to document the research activity conducted in the frame of a Ph.D. study regarding a proposal of an accident management strategy for a VVER-1000 nuclear power plant. Such a strategy called DEWS-AM, rely on a voluntary secondary side depressurisation followed by a primary side depressurisation. The main scope of the DEWS-AM is to maximize the so called ‘plant grace time’ in case of a Station Blackout event by proper operator actions, utilizyng the current NPP equipment. The strategy has been tested against two different plant status: at the beginning of a new cycle (new partial core and boron diluted in the coolant), in which large benefits have been obtained and an optimization method has been applied; at the end of a core cycle (no boron in the coolant), in which the recriticality issue has been covered too. The strategy results flexible enough to be applied to both core status positively impacting on the plant grace time (up to quadruplicate it comparing to a case in which any operator actions are taken). Even though the strategy may not become an accident managent procedure it can constitute the basis for AMP that relyes in external (but of limited capability) sources such as mobile pumps or mobile generators.